.222 Remington Magnum
|.222 Remington Magnum|
|Place of origin||USA|
|Parent case||.222 Remington|
|Bullet diameter||.224 in (5.7 mm)|
|Neck diameter||.253 in (6.4 mm)|
|Shoulder diameter||.357 in (9.1 mm)|
|Base diameter||.376 in (9.6 mm)|
|Rim diameter||.378 in (9.6 mm)|
|Case length||1.850 in (47.0 mm)|
|Overall length||2.280 in (57.9 mm)|
|Primer type||Small rifle|
|Maximum CUP||50,000  CUP|
|Test barrel length: 24"
Source(s): Hodgdon 
The .222 Remington Magnum was a short-lived commercially produced cartridge derived from the .222 Remington. Originally developed for a US military prototype Armalite AR-15 rifle in 1958, the cartridge was not adopted by the military, but was introduced commercially in sporting rifles.
The .222 Remington Magnum was created by lengthening the case and shortening the neck of the highly accurate and very popular .222 Remington cartridge, which dominated varmint and benchrest shooting during the 1950s. Case capacity is about 20% greater than that of the .222 Remington, producing moderately higher muzzle velocities. The .222 Remington Magnum served as the basis for the German developed 5.6 x 50 Magnum sporting cartridge.
It was not until 1963 that the Army adopted a .22 caliber (5.56 mm) assault rifle and cartridge, the M16 rifle and the 5.56 x 45 mm NATO cartridge. The .223 Remington, the commercial variant of the new 5.56 x 45 mm, was introduced a month before the official adoption of the military cartridge. The .223 Remington had a case capacity that is about 5% smaller than that of the .222 Rem. Mag., but it was loaded to a slightly higher pressure, so the ballistic differences are almost nonexistent. As any widely used military cartridge is guaranteed to be a success on the commercial market, the .223 Rem. sold exceptionally well and the .222 Rem. Mag. faded rather quickly. Remington continued to offer the .222 Rem. Mag. in a couple of target and varmint rifle models for many years, but currently (2007) there are no commercial manufacturers either of rifles or ammunition in .222 Rem. Mag. other than Cooper Firearms of Montana.
The .222 Rem. Mag. has not entirely gone, however. It lives on in the hands of handloaders and the original cartridge became the parent round for a new development introduced in 2004, the .204 Ruger. The .204 Ruger is based on the .222 Rem. Mag. case necked down to hold a .20 caliber (5 mm) bullet.
.222 Remington Magnum next to a .223 Remington cartridge.
- ".222 Remington Magnum". Accurate Powder. Western Powders Inc. Retrieved 21 September 2010. "http://www.accuratepowder.com/data/PerCaliber2Guide/Rifle/Standarddata(Rifle)/22Cal(5.56mm)/222%20Remington%20Magnum%20pages%20183%20and%20184.pdf"
- Hodgdon Online Reloading Data
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (September 2010)|
- .222 Remington and .222 Rem Mag at Chuck Hawks